Stamp duty on property transactions represents a nice little earner for George Osborne. Although the number of house sales is down by half since the top of the boom in the mid-2000s, the exchequer received more than £6bn from the tax in the 2011-12 financial year, a figure that is expected to double by 2017-18.

There are two big advantages of stamp duty as far as the Treasury is concerned: it is hard to avoid, and the take goes up as house prices rise and push properties into a higher band.

At the moment there is a big jump at the £250,000 level where stamp duty leaps from 1% to 3% – costing at least £5,000 in extra duty.

In much of the UK it will be a long time before the value of a home reaches £250,000. The regular surveys of the market from Halifax and Nationwide put the average house price between £160,000 and £170,000 a year. The latest monthly survey from the Land Registry suggests a similar figure.

This, however, gives a misleading picture according to the high-end property firm London Central Portfolio (LCP). It points out the quarterly data from the Land Registry, based on recent sales rather than historic data, puts the average UK property price at £249,958 – about what you would expect to pay for a flat in the capital.

A tiny increase in prices would, LCP says, see 80,000 buyers in 2013 – about 10% of the market – paying £7,500 in stamp duty rather than £2,500. That would be good news for first-time buyers if it artificially depressed prices and kept them within reach, but bad news if it clogged up the market by persuading sellers to sit tight rather than accept a lower asking price.

LCP suggests Osborne should raise the £250,000 threshold. With the Treasury counting every penny, there is zero chance of that happening.